Effects of alpha-efficiency variation on combined ESR/U-series dating of tooth fossil

Background: In combined Electron spin resonance (ESR)/U-series dating of tooth fossil, annual dose is comprised of the dose rate contributed by α-rays, β-rays and γ-rays. A correction factor (called alpha-efficiency or k-value) is applied to the measured or calculated alpha dose rate. However, due to the experimental difficulty, k-value could not be measured very precisely. Purpose: In order to investigate the effects of the two commonly used k-values and the variation on the dating results, we analyzed the tooth enamel samples from Longgupo, a hominid archaeological site in Chongqing. Methods: Five tooth fossils from Longgupo site were analyzed using combined ESR/U-series method, and their ages were calculated with DATA program. Results: The study showed that the sample ages decreased as k-value increased from 0 to 0.3. For the samples of low uranium concentration, the ages only had small changes (∼2%), while for those of high uranium concentration, the ages decreased obviously (up to 50%), and 20% decrement appeared when k-value increased from 0.13 to 0.23. For dating results of samples of similar uranium concentration, those of higher ²³⁰Th/²³⁴U ratio were affected more obviously with the k-value variation. Conclusion: The difficulty of measurement makes it hard to obtain a very precise k-value, and different k-values indeed cause considerable uncertainty to the fossil dating results. In addition, k-value may vary according to the uranium content of the tooth tissues, which will be investigated in further study. (authors)